1. Field of the Invention
The present invention relates to a scale for what is known as a bead bed and, more specifically, to a scale which is integrated into the frame of such a bed.
2. Background
Many patients, such as burn victims and immobile patients, must remain in bed for extended periods of time. When such patients lie on a conventional mattress, most of the patient's weight is born by protuberances of the posterior surface of the body such as the heels, the buttocks, the scapulae, and the occipital region of the head. As a result, the relatively small areas of soft tissue at such points are subjected to localized high pressures. When such localized pressures become great enough, the patient's small capillaries and veins in the tissue may collapse, causing pressure sores, decubitus ulcers and other circulatory complications. Burn patients may also risk extraction of skin grafts due to shearing or rubbing against the surface of a conventional mattress.
In order to overcome those problems and others, hospital beds have been developed which use fluidized granular material (preferably spherical beads coated with silicone) as a supporting medium in order to uniformly distribute the supporting pressure points along the body surface, thus reducing the pressure at the aforementioned critical areas. Beds employing such fluidized granular material are commonly referred to as "air fluidized" or "bead" beds.
Air fluidized beds typically comprise a tank partially filled with a substantial mass of granular material, such as spherical beads of fine soda ash coated with silicone to inhibit lumping. The granular material is supported directly on top of a diffuser board, and a flexible, loose fitting sheet such as a woven nylon, which is highly permeable to air but not the granular material, is laid on top of the granular material to form a patient support surface. Air is blown through the diffuser board into the granular material. Thence the gas flows (or bubbles) upwardly through the granular material and out the top of the tank through the cover sheet, thereby fluidizing the material so that a patient laying on the support surface is buoyantly suspended upon the bed. When the granular material is not being fluidized, the material settles down into a solid structure and contours to the body of a patient lying on the bed.
Fluidization of a bead bed evenly distributes the forces imparted on a patient's body and, as a result, the chance of circulatory complications such as decubitus ulcers is greatly reduced. Comfort for a supported patient is also enhanced, and movement of the fluidized support medium with the body helps to reduce the likelihood of skin graft extraction by eliminating or reducing shear. Also, the structure of such bead beds allows body fluids exuded from wounds to flow through the covering support surface and into the granular material away from the patient, quickening the healing process. The pH of the beads acts as an antibacterial agent and is not considered a good environment for bacteria.
Disclosure of such bead beds along with various features thereof can be found in U.S. Pat. Nos. 3,428,973; 3,485,240; 3,866,606; 4,498,205; 4,483,029; 4,564,965; 4,637,083; and 4,768,250. Said U.S. patents are incorporated herein in toto as examples of air fluidized beds which could use scales such as disclosed herein.
As is known to have been done with hospital beds, it has been considered desirable to equip such beds with a scale so that a patient supported thereon could be weighed in bed. The prior art includes a variety of scales for use in conjunction with hospital beds in general. For example, it has been known to provide scales, such as described in U.S. Pat. No. 4,281,730, onto which a hospital bed can be rolled in order to indirectly weigh the patient supported on the hospital bed. Other scales, such as described in U.S. Pat. No. 4,487,276, can be slid into place between a bed-ridden patient and a mattress in order to weight the patient. Another type of scale has employed load cell arrangements which require lowering of the patient support section of the bed onto load zone in order to weigh the patient. Still other scales, such as that disclosed in U.S. Pat. No. 4,793,428, have disclosed hospital beds with scale assemblies incorporated into the bed between the bed support frame and the patient supporting sections. Other examples of scales incorporated into the frames of various structures are disclosed in U.S. Pat. Nos. 4,023,633; 4,281,730; 4,487,276; 4,551,882; 4,629,015; 4,793,428; and 4,807,558, each of which are specifically incorporated herein by this reference in their entirety for any purposes of the disclosure of the present invention. Each of such types of scales have been somewhat effective for their intended purposes but either require some degree of movement of the patient or, when integrated into the structure almost inherently add some degree of instability to that structure.
The integration of a scale into a hospital bed is quite beneficial, especially for the purpose of weighing bed-ridden patients who are otherwise not able to stand on a conventional scale or who must be lifted from the bed with a sling or similar device to weigh. Movement of the patient is often difficult and may strain or injure medical personnel and may disturb or injure patient. Unfortunately, though, scales have not previously been integrated into the frame of a bead bed. Apparently, a reason for this is that the extreme weight of bead beds requires an exceptionally sturdy supporting frame. Common bead beds weigh almost a ton due to the great bulk of granular material that is required to evenly distribute the loads and fluidization beneath a supported patient. The great density of the commonly used granular materials also contributes to the weight of bead beds. Consequently, the added instabilities and weaknesses which are virtually inherent with bed scales have led those skilled in the art away from employing such scales in the frame of a bead bed.
Bead beds also present several obstacles relating to the required high sensitivity of a scale incorporated therein. Patient scales must be very accurate to give beneficial and useful indicators of weight change. Because of the great weight of a bead bed, a scale incorporated in the frame of a bead bed must be extra sensitive in order to accurately detect the relatively lesser weights of patients supported on the upper surface of the bed. In complete opposition to such sensitivity, though, the fluidization of a bead bed creates extraordinary vibrations due to ongoing displacement and re-displacement of masses of the granular material in tank 9 as air is bubbled therethrough. Vibrations are also caused by pinging due to the continuous collisions of the many tiny beads. Such vibrations caused by fluidization are far more significant than in other air beds such as low air loss beds. Additionally, any vibrations or waves encountered in a bead bed (including those originating from a patient thereon) are transmitted much more easily and perceivably through the solid granular material of bead beds than through the fluidized mediums of other hospital beds. To those skilled in the art of bead beds, such factors have made incorporating a scale in the frame of a bead bed for accurate weighing of the patient in situ seemingly impossible.
As a result, the only scales which have been considered feasible for employment in conjunction with beads beds have been those which are inserted above the granular material. Such insertable scales, though, inevitably interrupt or otherwise interfere with fluid flow between the granular material and the patient, and vice versa. Use of insertable scales also requires some movement of the patient in order to insert the scale beneath the patient's body, which inherently increases the risks of injury to such patients.
In sum, for a variety of reasons including the numerous factors opposing integration of a scale into the frame of a fluidized bead bed, those skilled in the art have been directed away from and, instead, have relegated themselves to the more cumbersome and more hazardous techniques of the prior art.